1. Field of Invention
This invention relates to methods and systems that indicate motion in a still image by inserting lines that indicate the trajectory of points of interest. More specifically, this invention is directed to methods and systems that automatically generate lines representative of the relative motion between an object and a background from a sequence of at least two video frames or fields.
2. Description of Related Art
Modern documents such as web pages, Microsoft(copyright) Word(copyright) files or PowerPoint(copyright) presentations can include motion through digital video or animations. New media are becoming increasingly available through network libraries, video conferencing, digital video camcorder and video capture devices. While these media can capture attention and communicate ideas, they are not compatible with printing.
It would be desirable to automatically represent motion information in a still image of a video signal so that the motion information is not lost when the still image of the video signal is displayed or printed.
This invention provides systems and methods that modify a still image of a video signal to represent motion in the still image
This invention separately provides systems and methods that modify the still image to represent motion adding motion lines representing the motion to one or more objects and/or background features within the still image.
This invention separately provides systems and methods that modify the still image by positioning the added motion lines representing the motion so the added motion lines extend from selected points of the still image.
This invention separately provides systems and methods that modify a still image to represent relative motion between an object in the foreground of the still image and the background of the still image.
This invention separately provides systems and methods that modify the still image to represent relative motion between a foreground object and a background of the still image by adding motion lines representing the motion to one or both of points on the foreground image and points of the background.
In one exemplary embodiment, the systems and methods of this invention align two or more successive video fields or video frames by distinguishing the motion between the fields or frames caused by moving the video camera from motion within the video fields or frames. The two types of motion are characterized. The individual video field or frames are transformed to align one of the fields or frames, usually the field or frame that is earlier in time, with the other base, field or frame.
The first type of motion, which is generally referred to as xe2x80x9cglobal motionxe2x80x9d, is due to movement of the camera between the fields or frames. Such movement is due to camera panning and/or zooming. The adjustment of one field or frame relative to a second field or frame necessary to generally align the features in these two fields or frames characterizes this global motion. A second type of motion, generally referred to herein as xe2x80x9clocal motionxe2x80x9d, refers to the movement of particular features between two fields or frames after the fields or frames are generally aligned for any global motion. This local motion is further characterized by the additional adjustments necessary to align these features between the two fields or frames. Once the motion between the two fields or frames is fully characterized for the features in the fields or frames, motion lines can be added to the later of the two or more fields or frames. The motion lines can be used to indicate the local motion, the global motion, or any desired combination of the global and local motion.
Global motion compensation is described in U.S. Pat. No. 5,784,115 to Gozde Bozdagi, incorporated herein by reference in its entirety.
In one exemplary embodiment of the systems and methods of this invention, where only local motion will be indicated by the motion lines, after compensating for global motion between the fields or frames, the local motion within the fields or frames can be detected. The local motion within the fields or frames is determined by taking a difference between intensity values at points of interest within the object in two successive video fields or frames. A binary mask of the region where the motion occurs is formed. The mask is formed by including only points in the base field or frame where the difference between intensity values exceeds a threshold value.
Points of interest are identified among the points included in the region of motion using various methods. In one exemplary embodiment of the systems and methods according to this invention, the points of interest are limited to those points positioned along edges. The edges are determined by identifying selected intensity gradients in the image values between a point of interest and points adjacent to that point of interest. Once the intensity gradients are determined, selected ones of the intensity gradients are selected. The selected gradients are greater than a predetermined threshold and are greater than the gradients at the adjacent points along the direction of the gradient.
In one exemplary embodiment of the systems and methods of this invention, the identified points of interest that lie on corners of features within the base field or frame are then selected from the identified points of interest. The points of interest lying on corners are identified by examining the image value of neighboring connected pixels and selecting a point of interest having a smaller number of neighboring connected pixels having a similar image value and a larger number of neighboring connected pixels having a different image value than that point of interest. Additionally, in another exemplary embodiment of the systems and methods of this invention, the selected points of interest are then selected so that the selected points of interest are spaced from each other by a predetermined minimum distance.
In one exemplary embodiment of the systems and methods of this invention, the motion of each selected point of interest is determined by first matching a block of pixels surrounding each of the selected points of interest in the later of two sequential video frames or fields with blocks of pixels at various positions in the former of the two sequential video frames or fields. The block of pixels that provides the minimum difference in intensities between the sequential video frames is determined. The motion is determined from the distance between the position of the block of pixels in the latter field or frame and the determined block of pixels in the former field or frame.
In another exemplary embodiment of the systems and methods of this invention, selecting the desired points of interest from among the identified points of interest includes adding a vector having N times the magnitude of the motion of an identified point of interest, where N is about 2, to the final position of the identified point of interest, and then determining whether the resulting point of interest falls within the region of motion. If the resulting point of interest does not fall within the region of motion, then the identified point of interest to which the vector was added is selected as a point of interest.
Lines representing the motion of the selected points are added to the latter field or frame. The added lines extend from the selected points of interest in the direction of the motion. The added lines have a direction and a length that represents the motion of the corresponding point of interest. Alternatively, these lines extend in a direction that is an average direction of the motion of all of the selected points. In this case, the length of each of the lines is proportional to the motion of its corresponding selected point.
The motion line adding systems and methods according to this invention produce a still image that includes a representation of the motion, between a plurality of fields or frames, of features within the field or frame. The motion is determined from a sequence of two or more video fields or frames that include the still image. In one exemplary embodiment, the motion line adding system includes a memory that stores captured and digitized fields or frames of an image that includes movement. A global motion system eliminates global motion between any two consecutive video fields or video frames. A candidate point determining circuit determines candidate points within a global-motion-compensated base field or frame stored in the memory. A motion determining circuit estimates motion occurring at the candidate points. A candidate point selector extracts selected points from the candidate points. A motion indicating circuit adds motion indicators to the still image at the selected points.
In another exemplary embodiment of the systems and methods of this invention, the motion mask can be generated by comparing two fields or frames without first adjusting for global motion between the two fields or frames. Thus, the motion mask is generated by comparing the uncompensated intensity values at the points of interest between the two fields or frames. In this case, the motion lines will indicate both the local and global motion between the two fields or frames.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.